Fastest speed in a piston engine aircraft over 15 km

On 23 April 2012, after taking off from Yolo County Airport in California, USA, pilot Will Whiteside (USA) flew over a 15-km stretch of the Interstate 505 highway, west of Sacramento, in his World War II-era Russian Yakovlev YAK-3 aircraft at an average speed of 614.02 km/h (381.53 mi/h). In doing so, Whiteside smashed the previous record of 467 km/h (290 mi/h) for a piston engine aircraft over 15 km (9.3 miles), set by Jim Wright (USA) in 1987 in a replica of Howard Hughes' (USA, 1905-76) H-1 Racer. According to the source, this record is for aircraft with piston engines that weigh between 3,858 and 6,614 lb (1,750 and 3,000 kg).

In September 1935 (52 years before Wright's record-breaking speed flight), Hughes himself achieved 566 km/h (352 mi/h) over 15 km but failed to establish the speed record because he entered the wrong weight in the paperwork! (Consultant doesn't state if that's the weight of the pilot or the plane.)